Find middle C and the octaves above and below it on a piano. If you are male you will use the octave below middle C, and if you are female you will use the octave above middle C.
Play each note descending or ascending (depending on whether you are male or female) from middle C until you complete an octave. As you play each note, reproduce it with your voice. Play and sing every note in the octave, paying attention to the facility with which you can sing each note. Some notes will feel more comfortable to sing than others.
Identify the note that you can sing most comfortably. This is your voice´s pitch. Knowing this will enable transposing of any accompanying instruments for the best vocal results.